Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ 59,714	$ 8,286	$ 237,906	$ (328,510)
Segment Assets	5,867,507		5,867,507		$ 5,636,387
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	348,368	335,617	1,292,944	1,159,943
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	30,123	(19,165)	98,972	(469,586)
Segment Assets	1,394,320		1,394,320		1,323,081
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	151,161	156,835	471,646	452,583
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	16,031	17,323	54,656	59,794
Segment Assets	1,732,632		1,732,632		1,680,734
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	50,049	52,998	156,212	162,627
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	21,643	22,795	66,389	68,272
Gathering [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	10,107	9,473	31,373	21,962
Segment Assets	568,115		568,115		534,259
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	34	65	86	303
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	26,853	25,417	82,629	65,601
Utility [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	4,348	2,179	51,103	52,745
Segment Assets	2,078,688		2,078,688		2,021,514
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	121,900	106,568	550,819	463,154
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	3,391	1,729	11,314	10,757
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(564)	(590)	2,122	4,117
Segment Assets	67,613		67,613		63,392
Energy Marketing [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	24,460	17,408	112,210	77,827
Energy Marketing [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	565	231	600	855
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	60,045	9,220	238,226	(330,968)
Segment Assets	5,841,368		5,841,368		5,622,980
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	347,604	333,874	1,290,973	1,156,494
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	52,452	50,172	160,932	145,485
All Other [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(98)	430	(498)	595
Segment Assets	76,560		76,560		77,138
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	538	1,508	1,311	2,775
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	(233)	(1,364)	178	1,863
Segment Assets	(50,421)		(50,421)		$ (63,731)
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	226	235	660	674
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (52,452)	$ (50,172)	$ (160,932)	$ (145,485)